Three dimensional vapor chamber

ABSTRACT

A three dimensional vapor chamber is disclosed which has a horizontal vapor chamber portion and a vertical flat heat pipe portion. The interiors of the two portions are in fluid communication and can have a wick material saturated with a working fluid such as water. The vertical flat heat pipe portion can also have fins or other heat exchange structure connected to the exterior thereof to increase heat transfer away from the heat pipe portion. In operation, the vapor chamber portion is placed in contact with a heat source, thus causing the working fluid to evaporate and move into the vertical flat heat pipe portion, where it is condensed. The fluid is then transported back to the vapor chamber portion via capillary action through the wick. The interiors of the two portions may be constructed as a vacuum chamber, so that evaporation of the working fluid can occur at lower temperatures than would occur at atmospheric pressure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.10/924,586, filed on Aug. 24, 2004, which is a continuation ofapplication Ser. No. 10/458,168, filed Jun. 10, 2003, now issued as U.S.Pat. No. 6,793,009, the entire contents of which are hereby incorporatedby reference in their entirety.

FIELD OF THE INVENTION

The invention relates to the management of thermal energy generated byelectronic systems, and more particularly to an improved thermal vaporchamber for efficiently and cost-effectively routing and controlling thethermal energy generated by various components of an electronic system.

BACKGROUND OF THE INVENTION

The electronics industry, following Moore's Law, has seemed to be ableto defy the laws of economics by providing ever increasing computingpower at less cost. However, the industry has not been able to suspendthe laws of physics inasmuch as high computing performance has beenaccompanied by increased heat generation. Board level heat dissipationhas advanced to a point that several years ago was only seen at thesystem level. The trend toward ever increasing heat dissipation inmicroprocessor and amplifier based systems, such as are housed intelecommunication and server port cabinets, is becoming increasinglycritical to the electronics industry. In the foreseeable future, findingeffective thermal solutions will become a major constraint for thereduction of system cost and time-to-market, two governing factorsbetween success and failure in commercial electronics sales.

The problems caused by the increasing heat dissipation are furthercompounded by the industry trend toward system miniaturization—one ofthe main methodologies of the electronics industry to satisfy theincreasing market demand for faster, smaller, lighter and cheaperelectronic devices. The result of this miniaturization is increasingheat fluxes. For example, metal oxide semiconductor-controlledthyristors may generate heat fluxes from 100 to 200 W/cm², some highvoltage power electronics for military applications may generate heatfluxes of 300 W/cm², while some laser diode applications require removalof 500 W/cm². Also, non-uniform heat flux distribution in electronicsmay result in peak heat fluxes in excess of five times the average heatflux over the entire semiconductor chip surface (˜30 W/cm²).

Thus, as clock speeds for integrated circuits increase, packagetemperatures will be required to correspondingly decrease to achievelower junction temperatures. However, increasing package temperatureswill result from the increase in heat dissipation in the package fromhigher clock speed devices. This increase in temperature will cascadethroughout the interior of the structure that encloses or houses suchcircuits, (e.g. a typical telecommunications or server port cabinets, orthe like) as the number of high power semiconductor componentspositioned within the housing increases. The difference between thesephysical aspects (i.e., the difference between the interior cabinettemperature and the package temperature) of the electronic systemdefines a “thermal budget” that is available for the design of thecooling devices/systems needed to manage the heat fluxes generated bythe various electronic devices in the system. As these two conflictingparameters converge, the available thermal budget shrinks. When thethermal budget approaches zero, refrigeration systems become necessaryto provide the requisite cooling of the electronic system.

It is well known to those skilled in the art that thermal resistances(often referred to as “delta-T”) for typical thermal systems at thesemiconductor junction-to-package, package-to-sink and sink-to-airlevels have been trending up over the past decade.

Extensive efforts in the areas of heat sink optimization (including theuse of heat pipes) and interface materials development in the past haveresulted in the significant reduction of sink-to-air and package-to-sinkthermal resistances. However, the reduction of these two thermalresistances has now begun to approach the physical and thermodynamiclimitations of the materials. On the other hand, the junction-to-packagethermal resistance (delta-T) has increased recently, due to theincreasing magnitude and non-uniformity (localization) of the heatgeneration and dissipation from the semiconductor package.

Successful cooling technologies must deal with thermal issues at thedevice, device cluster, printed wiring board, subassembly, and cabinetor rack levels, all of which are within the original equipmentmanufacturer's (OEM's) products. Many times, the problem is furthercomplicated by the fact that the thermal solution is many times an“after thought” for the OEM. A new equipment design may utilize thelatest software or implement the fastest new semiconductor technology,but the thermal management architecture is generally relegated to the“later phases” of the new product design. The thermal management issuesassociated with a given electronic system are often solved by theexpedient of a secondary cooling or refrigeration system that isarranged in tandem with the electronics system.

There are several negatives associated with the use of tandem cooling orrefrigeration systems. The additional electrical power required by suchsystems not only increases the cost to operate the electronic equipment,but also causes an adverse environmental impact in the form of pollution(from power generation processes) and noise. Reliability issues are alsoof considerable concern with refrigeration systems.

Thus, there is a compound challenge in the art to provide a thermalmanagement architecture that satisfactorily accumulates and transfersvariable amounts of thermal energy, generated by a wide variety ofelectronic components arranged together in an enclosed space, whileavoiding or minimizing the use of non-passive, tandem cooling orrefrigeration systems for cooling.

SUMMARY OF THE INVENTION

A vapor chamber is disclosed, comprising a vapor chamber portion and aheat pipe portion. Each portion can have a length measured in a firstdirection, a width measured in a second direction, and a height measuredin a third direction. Each portion further can comprise an inner cavityhaving a wick structure disposed on a surface of the cavity, the innercavities being in fluid communication with each other. The heat pipeportion can be disposed on the vapor chamber portion such that the widthof the heat pipe portion is substantially smaller than the width of thevapor chamber portion and the length of the heat pipe portion issubstantially equal to the length of the vapor chamber portion.

A three-dimensional vapor chamber comprising a vapor chamber portion anda heat pipe portion. The portions each can have a respective majorsurface comprising a substantially rectangular shape. The portionsfurther each can have an inner cavity comprising a wick, and the innercavities can be in fluid communication with each other. The heat pipeportion can be connected to the vapor chamber portion such that themajor surfaces are oriented substantially perpendicular to each other.Further, the lengths of the respective portions can be substantiallyequal as measured in a first direction, and the heights of therespective portions can be substantially different when measured in asecond direction substantially orthogonal to the first direction.

A three dimensional vapor chamber is disclosed, comprising first andsecond heat exchange chambers having inner cavities with wick structuresdisposed on respective inner surfaces thereof. The chambers can beconnected together so that the inner cavities are in fluid communicationwith each other. The first heat exchange chamber can have a length, awidth and a height as measured in first, second and third mutuallyorthogonal directions, respectively. The second heat exchange chambercan have a length, a width and a height as measured in the first, secondand third directions. The lengths of the first and second heat exchangechambers can be substantially equal, and the widths of the first andsecond heat exchange chambers can be substantially unequal.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate preferred embodiments of theinvention so far devised for the practical application of the principlesthereof, and in which:

FIG. 1 is a perspective view of the inventive vapor chamber assembly;

FIG. 2 is a side view of the vapor chamber assembly of FIG. 1;

FIG. 3 is a cross-sectional view of a portion of the vapor chamberassembly of FIG. 1, taken along line 3-3;

FIG. 4 is an end view of an alternative embodiment of the vapor chamberof FIG. 1, incorporating multiple vertical condenser portions withcooling fins mounted thereto.

DETAILED DESCRIPTION

This description of preferred embodiments is intended to be read inconnection with the accompanying drawings, which are to be consideredpart of the entire written description of this invention. The drawingfigures are not necessarily to scale and certain features of theinvention may be shown exaggerated in scale or in somewhat schematicform in the interest of clarity and conciseness. In the description,relative terms such as “horizontal,” “vertical,” “up,” “down,” “top” and“bottom” as well as derivatives thereof (e.g., “horizontally,”“downwardly,” “upwardly,” etc.) should be construed to refer to theorientation as then described or as shown in the drawing figure underdiscussion. These relative terms are for convenience of description andnormally are not intended to require a particular orientation. Termsincluding “inwardly” versus “outwardly,” “longitudinal” versus “lateral”and the like are to be interpreted relative to one another or relativeto an axis of elongation, or an axis or center of rotation, asappropriate. Terms concerning attachments, coupling and the like, suchas “connected” and “interconnected,” refer to a relationship whereinstructures are secured or attached to one another either directly orindirectly through intervening structures, as well as both movable orrigid attachments or relationships, unless expressly describedotherwise. The term “operatively connected” is such an attachment,coupling or connection that allows the pertinent structures to operateas intended by virtue of that relationship. In the claims,means-plus-function clauses are intended to cover the structuresdescribed, suggested, or rendered obvious by the written description ordrawings for performing the recited function, including not onlystructural equivalents but also equivalent structures.

Referring to FIGS. 1-3, the present invention comprises athree-dimensional vapor chamber 1 that is sized and shaped to transferthermal heat energy generated by at least one thermal energy source,e.g., a semiconductor device that is thermally engaged with a bottomsurface of the vapor chamber 1. The vapor chamber 1 has a horizontalevaporator portion 2 and a vertical condenser portion 4. The horizontalevaporator portion 2 comprises an inner cavity 3 defined between top andbottom walls 7, 11, and has a generally flat rectangular shape with aheight “h,” a width “w,” and a length “I.” The vertical condenserportion 4 can comprise an inner cavity 5 defined between opposing sidewalls 9, 13, and has a generally flat rectangular shape with a height“h1,” a width “w1,” and a length “l1.” The horizontal evaporator portion2 and the vertical condenser portion 4 are connected and hermeticallysealed so that their respective inner cavities 3, 5 form a single vaporspace.

The inner cavities 3, 5 of the evaporator and condenser portions 2, 4can have inner surfaces 22, 42 with a wick 50 disposed thereon. The wick50 can be saturated with a working fluid, and the inner cavities 3, 5can be maintained at a partial vacuum. Thus, as heat is applied to thebottom wall 11 of the evaporator portion 2, the working fluid (which maybe saturated in the wick 50) vaporizes, and the vapor rushes to fill thevacuum in the inner cavities 3, 5. Wherever the vapor comes into contactwith a cooler wall surface 42, it condenses, releasing its latent heatof vaporization. The condensed fluid then returns to the horizontalevaporator portion 2 via capillary action in the wick 50.Advantageously, employing capillary action as a fluid return mechanismallows the vapor chamber 1 to be used in any physical orientation,without respect to gravity, since capillary action can act to drive ordraw the working fluid “up hill.” Thus, the device will operateeffectively even if the installed upside down. It is noted thatproviding a wick is not critical, and thus the interior surfaces 22, 42of the vapor chamber 1 may be provided without a wick 50, particularlyin gravity-aided embodiments of the invention.

Thusly configured, the three dimensional vapor chamber 1 provides ahighly efficient means of spreading the heat from a concentrated source(through the bottom wall 11 of the evaporator portion 2) to a largesurface (the interior surfaces 22, 42 of the interior spaces 3, 5).Furthermore, the thermal resistance associated with the aforementionedvapor spreading is negligible as compared to traditional heat sinks.Further, the present design will provide increased cooling performanceas compared to typical vapor chamber designs which use multiple discretecylindrical “tower-type” condenser portions. This is because the presentdesign maximizes the cooling area (i.e. the wick-wall area), and alsothe volume, of the condenser portion by extending it all the way acrossthe length l of the evaporator portion 2. The “T-shape” of the presentinvention is also expected to perform better than vapor chambersincorporating multiple cylindrical “tower-type” condenser portionsbecause the condenser portion 4 of the present design retains asubstantial vertical dimension even if placed on its side. Vaporchambers utilizing multiple cylindrical “tower-type” condenser portionstypically are of limited to use in the vertical orientation, and alsoare limited in the amount of wick-wall area available for cooling. Thepresent design provides substantially more wick-wall area and vaporspace than prior devices, thus providing increased device efficiency.

The present invention is also expected to be less expensive and easierto manufacture than the prior designs, since the assembly process willrequire the attachment of a single condenser portion 4 (by welding,brazing or soldering) to the evaporator portion 2, rather than having toattach a multiplicity of individual small towers.

The top and bottom walls 7, 11 of the horizontal evaporator portion 2can comprise substantially uniform thickness sheets of a thermallyconductive material, and can be spaced-apart by about 2.0 (mm) to about4.0 (mm) so as to form the interior space 3 that defines the evaporatorportion 2. The top and bottom walls 7, 11 preferably comprisessubstantially planar inner surfaces 22, either or both of which can havean integrally formed wick 50 as previously noted. In one embodiment,sintered copper powder or felt metal wick structure, having an averagethickness of about 0.5 mm to 2.0 mm is positioned over substantially allof the inner surface of bottom wall 11 so as to form wick 50. Of course,other wick materials, such as, aluminum-silicon-carbide orcopper-silicon-carbide may also be used.

As previously described, to increase the thermal performance of thehorizontal evaporator portion 2, a vertical condenser portion 4 isconnected to the evaporator portion 2. More particularly, the verticalcondenser portion 4 comprises a flat rectangular structure similar tothat of the evaporator portion 2. Specifically, first and second sidewalls 9, 13 can comprise substantially uniform thickness sheets of athermally conductive material, and are spaced-apart by about 2.0 (mm) toabout 4.0 (mm) so as to form the inner space 5 that defines thecondenser portion 4. The side walls 9, 13 preferably comprisesubstantially planar inner surfaces 42, while the top wall 15 is alsosubstantially planar. The condenser portion 4 is open at its bottomextremity 17 where it connects to a correspondingly sized opening 19 inthe top wall 7 of the horizontal evaporator portion 2.

The walls of the evaporator and condenser portions 2, 4 can behermetically sealed at their respective joining interfaces to preventleakage of the working fluid, and to maintain partial vacuum conditionswhere appropriate.

The interior surfaces 42 of the top and side walls 9, 13, 15 cancomprise an integrally formed wick 52, similar to that described inrelation to wick 50 of the evaporator portion 2. Alternatively, theinterior surfaces 42 of the condenser portion 4 can have no wick, oronly portions of the interior surfaces may be provided with a wick 52.For example, where the vapor chamber 1 is oriented such that thecondenser portion 4 is located above the evaporator portion 2, it maynot be required to provide wick material to the inner surfaces of thecondenser portion 4 because gravity may provide the necessary force toreturn condensed liquid to the evaporator portion 2. On the other hand,if the evaporator portion 2 is located at or above the level of thecondenser portion 4, it will likely be appropriate to provide wickmaterial over at least a portion of the inner surfaces 42 of thecondenser portion 4. For applications in which the orientation of thevapor chamber may be variable, such as in aircraft or spacecraftapplications, it may be appropriate to provide wick material to most orall of the interior surfaces 42 of the condenser portion 4. It should benoted that in the preferred embodiment of the present invention, no wickstructure is present in the top wall 15 of the condenser portion 4.

Where a wick is provided for both the evaporator and condenser portions2, 4, it can be the same material, thickness, etc. for both portions.Alternatively, different wick designs and/or materials can be used foreach of the condenser and evaporator portions (or for limited areas oneach), depending on the use and installed orientation of the vaporchamber 1.

In addition to the wick materials and configurations previouslydiscussed, the wicks 50, 52 may also comprise screens or groovesintegral with any of the interior surfaces 22, 52 of the evaporatorportion 2 or condenser portion 4. Further, a plastic-bonded wick can beapplied simultaneously and as a contiguous structure after thestructural elements of the evaporator portion 2 and condenser portion 4are connected together. This could provide a contiguous fluid conduitbetween the evaporator and condenser regions of the device, which may beadvantageous when the evaporator is elevated.

In a further embodiment, a brazed wick may be formed on any of the innersurfaces of evaporator or condenser portions 2, 4, as desired. Dependingon the heat load and particular power density, other wick structures mayalso be appropriate. Examples of such structures include screen bondedto the input surface by spot-welding or brazing a monolayer of powdermetal, grooves cut in the surface 22, 42 of either portion 2, 4, or anarray of posts, either of the all-powder variety or solid copper whichis powder covered, or brazed to the wall, which in a preferredembodiment would be copper material.

The working fluid may comprise any of the well known two-phasevaporizable liquids, e.g., water, alcohol, freon, methanol, acetone,fluorocarbons or other hydrocarbons, etc.

The vapor chamber 1 is formed according to the invention by drawing apartial vacuum within the interior spaces 3, 5 and then back-fillingwith a small quantity of working fluid, e.g., just enough to saturatewick 50 just prior to final sealing of the spaces 3, 5 by pinching,brazing, welding or otherwise hermetically sealing, once the condenserportion 4 is mounted to the evaporator portion 2 such that theiropenings 17, 19 align. The atmosphere inside the vapor chamber 1 is setby an equilibrium of liquid and vapor.

In practice, a heat source (not shown) is mounted to the bottom wall 11of the evaporator portion 2. Heat from the heat source is conductedthrough the wall 11 causing the working fluid in wick 50 to evaporate.The vapor travels through the inner space 5 in the condenser portion 4,where it contacts the wick 52 and/or inner surfaces 42 of walls 9,13,15.The vapor condenses on the walls, giving up its latent heat throughcondensation. The condensate then returns to the evaporator portion 2 bygravity, or through capillary action of the condenser portion wick 52(if provided) and/or the evaporator portion wick 50.

An alternative embodiment of a vapor chamber 10 is shown in FIG. 4, inwhich the vapor chamber 10 has an evaporator portion 20 and a pair ofparallel-oriented condenser portions 40. The condenser portions 40 canbe configured similarly to the condenser portion 40 described inrelation to the vapor chamber 1 of FIGS. 1-3, including wick materialsand arrangements, etc.

Referring again to FIG. 1, a pair of folded fin assemblies 100, 102 canbe provided on opposite sides of the condenser portion 4 of vaporchamber 1. The folded fin assemblies 100, 102 each can comprise aplurality of substantially parallel, thin fin walls 112 separated fromone another by alternating flat ridges 114 and troughs 120. Each pair ofthin fin walls 112 are spaced apart by a flat ridge 118 so as to formeach trough 120 between them. Thus folded fin assemblies 100, 102comprises a continuous sheet of thermally conductive material foldedinto alternating flat ridges 114 and troughs 120 defining spaced thinfin walls 112 having peripheral end edges 122. A spacer 60 can bepositioned between the top wall 7 of the evaporator portion 2 and thebottom-most fin wall 112 to support the folded fin assembly at eachcorner of the evaporator portion 2. Advantageously, fin walls 112 have athickness that is no more than about 0.020″, and in a preferredembodiment have a thickness in the range from about 0.002 to 0.020inches. In this way, the thermal impedance of fin walls 112 to theconduction of thermal energy is in a range of no more than about2.5×10^(−3 ÿ)c/w/cm² to about 2.54×10^(−2 ÿ)c/w/cm² for aluminummaterial. Materials other than aluminum can also be used, such asmetals, polymers, etc.

The monolithic extended geometry of the condenser portion 4 makes thefolded fin assemblies 100, 102 efficient and easy to manufacture andassemble to the vapor chamber 1, allowing the assemblies to cool thecondenser portion all along the flat length of the condenser andevaporator portions 2, 4. Again, this is in contrast to prior designshaving multiple cylindrical “tower-type” condenser portions, which arenot configured for use with simple rectangular folded fin assemblies, orwhich if used with such assemblies would not allow contact along theentire outer surface of the condenser portion.

Alternatively as shown in FIG. 4, an array of plate fins 130 can bemounted to the condenser portion 4 to convey the heat to the ambientenvironment, similar to the folded fin arrangement.

A forced air system can also be provided to move air through the troughsof the folded fin assemblies. For example, a fan could be mountedadjacent to one end of each of the folded fin assemblies to blow airthrough the troughs at a desired rate. Other similar forced coolingarrangements could also be provided.

Accordingly, it should be understood that the embodiments disclosedherein are merely illustrative of the principles of the invention.Various other modifications may be made by those skilled in the artwhich will embody the principles of the invention and fall within thespirit and the scope thereof.

1. A vapor chamber comprising: an evaporator portion having a lengthmeasured in a first direction, a width measured in a second direction,and a height measured in a third direction, the evaporator portionfurther having a cavity; and a condenser portion having a lengthmeasured in the first direction, a width measured in the seconddirection, and a height measured in the third direction, the condenserportion further having a cavity; wherein a wick structure is disposed ona surface of at least one of the cavities, the portions being connectedso that the cavities are fluid communication with each other; andwherein the condenser portion is connected to the evaporator portion sothat the width of the condenser portion is substantially smaller thanthe width of the evaporator portion and the length of the condenserportion is substantially equal to the length of the evaporator portion.2. The vapor chamber of claim 1 wherein the height of the condenserportion is substantially greater than the height of the evaporatorportion.
 3. The vapor chamber of claim 1 further comprising a heatdissipating structure in contact with an outer surface of the heat pipeportion.
 4. The vapor chamber of claim 3 wherein the heat dissipatingstructure comprises a folded fin heat exchange structure comprising aplurality of heat exchange cavities disposed adjacent the outer surfaceof the condenser portion.
 5. The vapor chamber of claim 4 furthercomprising a forced air system for providing forced air flow through atleast a portion of the heat exchange cavities.
 6. The vapor chamber ofclaim 2 wherein the inner cavities of the evaporator and condenserportions are hermetically sealed and at least a partial vacuum createdwithin the cavities.
 7. The vapor chamber of claim 6 further comprisinga working fluid, wherein the working fluid is disposed within at least aportion of the wick structure of the evaporator portion.
 8. Athree-dimensional vapor chamber comprising: a evaporator portion and acondenser portion, the portions each having a respective major surfacecomprising a substantially rectangular shape, the portions further eachhaving an inner cavity comprising a wick, the inner cavities being influid communication with each other; wherein the condenser portion isconnected to the evaporator portion such that the major surfaces areoriented substantially perpendicular to each other; and wherein thelengths of the respective portions are substantially equal as measuredin a first direction, and the heights of the respective portions aresubstantially different when measured in a second directionsubstantially orthogonal to the first direction.
 9. The vapor chamber ofclaim 8 wherein the evaporator portion has a width as measured in athird direction, the condenser portion has a width as measured in thethird direction, the third direction being substantially orthogonal toboth the first and second directions, and the width of the condenserportion being substantially smaller than the width of the evaporatorportion.
 10. The vapor chamber of claim 8 further comprising a heatdissipating structure in contact with an outer surface of the condenserportion.
 11. The vapor chamber of claim 10 wherein the heat dissipatingstructure comprises a folded fin heat exchange structure comprising aplurality of heat exchange cavities disposed adjacent the outer surfaceof the condenser portion.
 12. The vapor chamber of claim 11 furthercomprising a forced air system for providing forced air flow through atleast a portion of the heat exchange cavities.
 13. The vapor chamber ofclaim 9 wherein the inner cavities of the evaporator portion and thecondenser portion are hermetically sealed and at least a partial vacuumis created within the cavities.
 14. The vapor chamber of claim 13further comprising a working fluid, wherein the working fluid isdisposed within at least a portion of the wick structure of theevaporator portion.
 15. A three dimensional vapor chamber comprising:first and second heat exchange chambers having inner cavities with wickstructures disposed on respective inner surfaces thereof, chambers beingconnected together so that the inner cavities are in fluid communicationwith each other; the first heat exchange chamber having a length, awidth and a height as measured in first, second and third mutuallyorthogonal directions, respectively; and the second heat exchangechamber having a length, a width and a height as measured in the first,second and third directions; wherein the lengths of the first and secondheat exchange chambers are substantially equal, and the widths of thefirst and second heat exchange chambers are substantially unequal. 16.The vapor chamber of claim 14 wherein the width of the first chamber issubstantially smaller than the width of the second chamber.
 17. Thevapor chamber of claim 14 further comprising a heat dissipatingstructure in contact with an outer surface of the first chamber.
 18. Thevapor chamber of claim 17 wherein the heat dissipating structurecomprises a folded fin heat exchange structure comprising a plurality ofheat exchange cavities disposed adjacent the outer surface of the firstchamber.
 19. The vapor chamber of claim 18 further comprising a forcedair system for providing forced air flow through at least a portion ofthe heat exchange cavities.
 20. The vapor chamber of claim 15 furthercomprising a working fluid, wherein the working fluid is disposed withinat least a portion of the wick structure of the second chamber.